Design Mode Note: Singleton mode (C ++ code)

Definition:
A class has only one instance and provides a global access point to access it.
Key points:
1. The class can only have one instance;
2. You must create this instance on your own;
3. You must provide this instance to the entire system.

Implementation 1: Singleton mode structureCode

Singleton. h:

View code

# Ifndef _ singleton_h _# Define_ Singleton_h _ClassSingleton {Public:StaticSingleton *Getinstance ();Protected: Singleton ();Private:StaticSingleton *_ Instance ;};# Endif
 

Singleton. cpp:

View code

# Include " Singleton. h  "  # Include <Iostream> Using   Namespace  STD; Singleton * Singleton: _ instance = 0  ; Singleton: Singleton () {cout < "  Create Singleton...  " < Endl;} Singleton * Singleton: getinstance (){  If ( 0 = _ Instance) {_ instance = New  Singleton ();}  Else  {Cout < "  Already exist  " < Endl ;}  Return  _ Instance ;} 

Main. cpp:

# Include"Singleton. h"IntMain () {Singleton* T =Singleton: getinstance (); t->Getinstance ();Return 0;}
 

Implementation 2: printer instances

Singleton. h:

View code

 # Ifndef _ singleton_h _  # Define _ Singleton_h _ Class  Singleton {  Public :  Static Singleton * Getinstance ();  Void Printsomething ( Const   Char * Str2print );  Protected  : Singleton ();  Private  :  Static Singleton * _ Instance;  Int  Count ;}; # Endif 

Singleton. cpp:

View code

# Include "  Singleton. h  "  # Include <Iostream> Using   Namespace  STD; Singleton * Singleton: _ instance = 0  ; Singleton: Singleton () {cout < "  Create Singleton... " < Endl; count = 0  ;} Singleton * Singleton: getinstance (){  If ( 0 = _ Instance) {_ instance = New  Singleton ();}  Else  {Cout < " Instance already exist  " < Endl ;}  Return  _ Instance ;}  Void Singleton: printsomething ( Const   Char * Str2print) {cout < "  Printer is now working, the sequence:  " <++ Count < Endl; cout <Str2print <Endl; cout < "  Done \ n  " < Endl ;} 

Main. cpp:

# Include"Singleton. h"IntMain () {Singleton* T1 =Singleton: getinstance (); T1->Getinstance (); T1-> Printsomething ("T1"); Singleton* T2 =Singleton: getinstance (); T2-> Printsomething ("T2");Return 0;}
 

MAKEFILE file:

Cc = g ++Cflags=-G-O2-wallall: Make singletonsingleton: Singleton. O \Main.O$ {CC}-O Singleton main. O Singleton.Oclean: Rm-RF Singleton Rm-f *.O. Cpp.O:$ (CC) $ (cflags)-c-o $ *. o $ <
 

Running effect:

We can see that the count of the print order count is continuous, and there is only one printing device in the system.